Julia Michaels, who has co-written hits for Justin Bieber, Selena Gomez and Hailee Steinfeld, talks stepping out on her own with 'Nervous System.'Catie Laffoon

On a Los Angeles morning, as the temperature climbs toward the triple digits, Julia Michaels rolls up for breakfast at a spot on Ventura Boulevard not far from her home, wearing a black turtleneck, floral-printed pants and one of the 16 pairs of Doc Martens she owns. "I never know how to dress for the right temperature," she explains. At the curb sits her gray Ford Escape. "My mom car. I love it."

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It's not exactly the cruising vessel you'd imagine for a 23-year-old who has co-written a string of nine Hot 100 hits, including Justin Bieber's "Sorry," Selena Gomez's "Hands to Myself," Nick Jonas and Tove Lo's "Close," and "Issues," the song that marked Michaels' transition from songwriter to singer, and which has been comfortably lodged in the Top 50 for months. For the past two years, Michaels has been a crucial force in edging mainstream pop away from insistent party anthems toward a more personal place. It was Michaels who thought Gomez's "Hands to Myself" should sound like Prince; Michaels who sparked the concept for Hailee Steinfeld's "self-care" anthem "Love Myself," when, after a nap failed to shake jet lag during a Stockholm writing trip, Michaels announced to songwriting partner Justin Tranter, "I masturbated, so I feel so much better"; and Michaels who wanted to write over the bass line of Talking Heads' "Psycho Killer," resulting in Gomez's recent hit "Bad Liar," a minimalist alternative to the 24-karat magic of current pop.

Michaels picks up the spare catchiness of "Bad Liar" on her seven-song debut, Nervous System, from the glammy come-ons and acoustic-guitar snap of "Uh Huh" to the solo-piano heartbreak ballad "Don't Wanna Think." "The music is very simple – just an added texture to tell the story," says Michaels. Nothing gets in the way of the melodies or lyrics. "I'm a perfectionist and like things clean and in their space."

When Michaels was about five, her family moved from Davenport, Iowa, to Santa Clarita, California, 40 miles north of L.A., in part so her father could pursue his acting dreams. After her parents split up, her mom thought Julia might take to acting and shuttled her to auditions. She was more interested in putting her poems to music, but her sister was the singer in the family. At one of her sister’s sessions, 15-year-old Julia sang for Joleen Belle, who wrote songs for TV and movies. Belle asked her to collaborate, and when they landed the theme song to the Disney TV show Austin & Ally in 2011, Michaels was on her way. Cuts for Demi Lovato and Gomez followed. Two years ago, Gomez invited Michaels and Tranter on a writing trip to Puerto Vallarta, Mexico. She ended up contributing to seven of the 11 tracks on Gomez’s Revival, which debuted at Number One.

When Michaels was about five, her family moved from Davenport, Iowa, to Santa Clarita, California, 40 miles north of L.A., in part so her father could pursue his acting dreams. After her parents split up, her mom thought Julia might take to acting and shuttled her to auditions. She was more interested in putting her poems to music, but her sister was the singer in the family. At one of her sister's sessions, 15-year-old Julia sang for Joleen Belle, who wrote songs for TV and movies. Belle asked her to collaborate, and when they landed the theme song to the Disney TV show Austin & Ally in 2011, Michaels was on her way. Cuts for Demi Lovato and Gomez followed. Two years ago, Gomez invited Michaels and Tranter on a writing trip to Puerto Vallarta, Mexico. She ended up contributing to seven of the 11 tracks on Gomez's Revival, which debuted at Number One.

Michaels' vocals on demos of songs for Steinfeld led Charlie Walk, president of Republic Records, to ask why she wasn't recording herself. She was, she says, too insecure. The studio was her safe space. But in the end, "Issues" – a song about the push and pull of a relationship electrified by jealousy, anger and need – was too personal to let anyone else sing. "I think I'm done hiding," she told Walk.

Like most of Michaels' work, the seven songs on Nervous System are about lust that won't quit, and the problems that follow love. "She is so willing to admit everything about herself," Tranter says. "The good things and bad things."

"I'm not a big drinker, I don't really party, I'm kind of a hermit," Michaels says. "I'm such a relationship person. I just lose myself in that person. And that is all I know how to write about in those moments." But songs like "Just Do It" ("Don't let me down gently") and "Don't Wanna Think" ("I thought that we were good enough/I thought that you needed love") find her reflecting on when relationships go wrong. "I just went through a breakup," she says. "Ani DiFranco's 'Independence Day' has really been getting me through it." After breakfast, she's maybe going to get in her Ford Escape and just drive, looping the song over and over. "Crying. A lot. But it's one of the best songs on the planet." Somewhere, chances are, someone is using one of her songs the same way.